Sudden Manifestation: PCs that don't succeed on a hard (DC 20) Wisdom "Perception" check can't react to the sudden manifestation of the cold ones. Place them anywhere nearby and let them act on surprise. PCs who make the check can act on initiative as normal.

Flight: Cold ones are drifting through the air, not fast but free.

Semi-Incorporeal: Cold Ones are only somewhat corporeal creatures. They cannot pass through solid materials but can squeeze through the tiniest holes.